Storage systems coupled to multiple host computers have highly-frequently accessed areas called “hot spots” where accesses concentrate to specific data. Recent virtualization techniques enable multiple virtual machines to be operated in the host computers, so that a configuration is possible where a large number of virtual computers several tens of times greater than the number of physical computers actually coupled to the storage system access the storage system.
According to the storage subsystem coupled to such computer system, it is assumed that multiple hot spots occur simultaneously in a scattered manner in virtual disks accessed by virtual machines, and the number of hot spots is considered to increase in proportion to the number of coupled virtual machines. In order to cope with such hot spots from the storage subsystem side, it may be possible to adopt a semiconductor storage device (SSD: Solid State Drive) capable of responding at a higher speed than the prior art HDD (Hard Disk Drive) as a single storage media used in the storage system.
An even higher transmission speed is enabled by mounting a multilink SAS connector (SFF-8630 (corresponding to 2×2 wide port) or SFF-8639 (corresponding to 2×4 wide port)) capable of acting as a wide port device to the SSD. However, since the SSD has a bit cost with respect to the storage capacity that is more expensive than the HDD, a technique for suppressing arrangement costs such as via storage tier control is adopted. Further, in a purpose of use putting more value on performance than on cost, a technique is adopted to use the SSD and the semiconductor memory board as an expansion of the cache memory in the storage subsystem. Patent Literatures 1 and 2 teach techniques related to the above-described art.